Almost Everything you wanted to know about using S2PLOT to visualise astronomy datasets

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(Almost) Everything you wanted to know about
using S2PLOT to visualise astronomy datasets
CRICOS provider 00111D
Christopher Fluke David Barnes
Those not properly initiated into the mysteries
of visualisation research often seek to
understand the images rather than appreciate
their beauty... Al Globus Eric Raible (1994)
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What is Visualisation?
Visualisation System
Knowledge discovery
Data
Science

• The process of creating (computer-generated)
  images in order to gain new understanding or
  insight into data.

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Astronomical Data

• Brunner et al. (2001)
• Imaging data 2D, narrow ??, fixed epoch
• Catalogs secondary parameters determined from
  processing (coordinates, fluxes, sizes, etc).
• Spectroscopic data and products (e.g. redshifts,
  chemical composition).
• Studies in the time domain - moving objects,
  variable and transient sources (synoptic surveys)
  
• Numerical simulations from theory

Planning, data collection, reduction,
comprehension Many astronomical datasets have N gt
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The rest of this presentation...

• What is S2PLOT?
• Getting started
• Geometry
• Points, lines, coordinates, labels, text
• Spheres, cubes, polygons
• Colour and colour maps
• Static versus dynamic geometry S2PLOT callbacks
• Billboards/splats
• Handles
• Nice fonts
• Volume rendering, isosurfaces
• Other media
• 3d-PDF, Web, s2slides

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Introducing S2PLOT

• AIM to enable visualization-led scientific
  discovery
• BY making an easy-to-use programming library
• THAT WORKS ON the astronomers desktop
  workstation
• AND WITHOUT RECOMPILATION ON advanced display
  devices
• RESULT
• S2PLOT Barnes et al., 2006, PASA, 23, 82
• www.astronomy.swin.edu.au/s2plot (Version 2.4)

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Key Features and Benefits

• Supports standard and enhanced displays
• Real-time interaction
• Mouse keyboard navigation
• Static and dynamic data
• Runs on Apple/OSX, GNU/Linux and Windows
  (GNU/cygwin)
• C/C, Fortran and Python
• PGPLOT-inspired programming interface

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A Practical Example
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A Practical Example
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A Practical Example
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A Practical Example
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A Practical Example

• 2-d views of multi-d data
• Colour-colour
• Colour-magnitude

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A Practical Example
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S2PLOT Program Flow
Handle window events
Handle user events
Process callbacks
Draw geometry using OpenGL lists
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An easy s2plot program (in C)
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An easy s2plot program (in C)
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An easy s2plot program (in C)
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An easy s2plot program (in C)
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An easy s2plot program (in C)
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An easy s2plot program (in C)
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Comiple and Execute

• Configure your S2PLOT environment...
• cbuild.csh s2example
• ./s2example

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Programming Reference
http//astronomy.swin.edu.au/s2plot
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Sample code for every function
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PGPLOT versus Native functions
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Example Points and lines
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Example spheres and polygons
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Example text
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Static versus Dynamic geometry

• Static geometry
• Draw it once
• Dynamic
• Redraw on every display refresh
• Animation!
• Advanced interaction mouse click events, key
  presses, iPod
• Geometry that depends on camera angle
• Callbacks

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Billboards Splats

• Billboards (2-d) things which always face the
  camera
• good for labels markers
• Splats billboards which are soft point-like
  textures (images)
• visually appealing alternative to single-pixel
  points
• star fields, stellar clusters
• variable size and colour with good blending
  properties
• simulated particle distributions
• thresholded, gridded volume data
• Billboards have to be redrawn whenever the camera
  moves, so they must only be created in a callback
  function.

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Billboards Splats Example
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Nice Fonts

• As in PGPLOT, the basic font in S2PLOT is a
  "Hershey" font
• vector-based
• functional fast, but inelegant
• S2PLOT provides 2 better ways to create text
  labels
• unsigned int ss2ltt(char latexcmd, float
  aspect)
• uses LaTeX to generate a bitmap which is
  converted into an S2PLOT texture for you.
  (Requires a few environment variables to be set
  correctly - see ENVIRONMENT.TXT in S2PLOT)
• nice for equations
• unsigned int ss2ftt(char fontfilename, char
  text, int fontsizepx, int border)
• uses the FreeType2 font engine to generate a
  bitmap which is converted into an S2PLOT texture
  for you.

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Nice Fonts Example
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Handles

• Handles provide user interaction
• they can be displayed or hidden with Shift-S
• your code can be alerted when a handle is clicked
  on
• your code can be alerted when a handle is dragged
• Handles have
• a position in 3-d space, and a size (fraction of
  the screen)
• a texture and colour for their "unselected" state
• a texture and colour for their "selected" state
• You can make invisible handles and draw other
  geometry at their location if you want.

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Handles (continued)

• Possible uses for handles
• select points in a displayed dataset
• select galaxies or stars or planets in a
  visualisation
• define a 3-d region (volume selection)
• provide buttons and sliders and even menus
• this is typically done in "screen coordinates"
  mode
• allow users to define control points along a
  spline camera path
• etc.

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Isosurfaces and Volume Rendering
Data courtesy J.English
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Colour maps

• Computers generate colours through R G B
  combinations
• 24-bit RGB 16,777,216 (256³ or 224) colours

• Colour can enhance important features
• Can exaggerate unimportant details
• Try different colour maps

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Other media

• 3-d PDF
• Barnes, D.G., Fluke, C.J. 2008, Incorporating
  interactive 3-dimensional graphics in astronomy
  research papers, New Astronomy, 13, 599
• Fluke, C.J., Barnes, D.G. 2008, The Interactive
  Astronomy Textbook, Astronomy Education Review,
  7, 113
• Web
• Fluke, C.J., Barnes, D.G., Jones, N.T. 2009,
  Interchanging Interactive 3-d Graphics for
  Astronomy, Publications of the Astronomical
  Society of Australia, accepted, arXiv0810.4201F
• s2slides PowerPoint-style presentations

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Where to next?

• Try some S2PLOT sample code
• http//astronomy.swin.edu.au/s2plot
• Take part in the hands-on workshop
• Talk to me about your data